This invention relates to spark wheels and thumb control means for rotation of said spark wheels for use in cigarette lighters and the like, and more particularly to a unitary, one-piece spark and thumb wheel construction and a method for manufacturing the same.
In order to properly function, a spark wheel must incorporate an abrasive surface which, when rotated against a flint or similar pyrophoric material, will produce a spark to ignite a fuel-fed wick or jet of flammable gas. As is well-known in the art, before the abrasive surface can be formed, substantially parallel grooves must be formed in the cylindrical surface of the spark wheel body at an acute angle to the sides of the wheel in order to provide the proper offset spacing for the cutting edges of the spark wheel.
The two well-known prior art methods for producing the desired abrasive surface for the spark wheel are chiseling and broaching. The most commonly used prior art process is the chiseling process, in which the grooved spark wheel is rotated while a chiseling tool or blade reciprocatingly cuts into the peripheral surface of the spark wheel as the spark wheel is rotated about its central axis. The chiseling process forms a plurality of substantially linearly arranged inclined teeth in the surface of the spark wheel. This, in combination with the grooves which have been previously cut into the spark wheel surface, produces the required abrasive surface for the spark wheel. However, in order to provide sufficient support for holding the spark wheel and rotating the spark wheel during the chiseling process, a hole is formed completely through the center of the spark wheel in order to provide the required holding and rotating surface.
The second known process for producing spark wheels is disclosed in U.S. Pat. No. 2,455,348. As shown therein, the grooved cylindrical wheel is pushed through a broaching die to produce the desired abrasive surface for the spark wheel. Although a central hole or cavity is not required in order to achieve the broaching action, the produced spark wheel can only have a single diameter, namely the diameter of the desired spark wheel. As a result, a central cavity or hole is formed in the spark wheel in order to provide a surface for mounting the spark wheel in a lighter and for cooperatively mounting the necessary thumb rotation-inducing members.
Generally, once the spark wheel has been manufactured with its abrasive peripheral surface, two substantially identical discs, incorporating a spark wheel mounting shelf extending therefrom, are secured on either side of the spark wheel. The mounting shelves are constructed so as to be press-fitted into the central cavity or hole of the spark wheel, thereby achieving secure frictional engagement between the disc and the spark wheel.
Furthermore, the discs incorporate mounting pins extending from the opposite side of the spark wheel holding shelf which allow the spark wheel-disc assembly to be mounted in a lighter. Also, the discs incorporate an outer peripheral surface which is scored or ratchet-like in order to provide a gripping surface which allows the thumb of the user to rotate the discs in order to cause the spark wheel to rotate against the flint causing a spark which ignites the desired flame.
Many difficulties have been encountered in the prior art with the combination spark wheel and thumb wheel assemblies. One major difficulty repeatedly encountered is the inability of the mounting shelf of the thumb wheel to remain firmly frictionally engaged with the walls of the central cavity of the spark wheel. As a result, when the user of the lighter rotates the thumb wheel, the frictional force necessary to overcome the resistance of the spark wheel to rotate against the flint and cause the spark is greater than the frictional engagement between the spark wheel cavity and the thumb wheel mounting shelves. As a result, the thumb wheels rotate but the spark wheel does not. Obviously, this results in a cigarette lighter which is completely unfunctional.
Another major difficulty encountered with the prior art assemblies is the plurality of separate parts that are required and the cost of assembling these various parts into an operable unit mounted in a lighter system. One of the primarily important assembly steps is the positioning of the spark wheel with the proper orientation to provide a spark when rotated towards the flammable gas. Since identically sized thumb wheels are mounted on both sides of the spark wheel, the assembler of the lighter must visually check each spark wheel and thumb wheel assembly to be certain that the orientation of the spark wheel abrasive surface is proper before mounting this assembly in the lighter. This results in an extremely costly assembly operation. Furthermore, the plurality of separate parts and the various operations which must be performed on these parts requires repeated handling during the production process, thereby causing extremely high production costs.